1. Field of the Invention
The present invention relates to an optical disk device that makes control so that the data recording layer of an optical disk will be perpendicular to the optical axis of laser light irradiated onto the optical disk.
2. Description of the related art
As long as the optical axis of laser light irradiated from an optical pickup is constantly perpendicular to the target data recording layer of an optical disk, the laser light formed for recording/reproduction on the track of the optical disk is correctly focused on the data recording surface. Coma does not occur so that the beam spot diameter of laser light is smallest on the data recording layer so that sufficient read/write quality is obtained.
An optical disk may be subjected to distortion or warp in accordance with various process conditions or management state such as the temperature, pressure or cooling period during its resin molding. Such an optical disk is accompanied by a problem of tilt that the optical axis of laser light irradiated from an optical pickup is not perpendicular to the target data recording layer of an optical disk. When the permissible tilt range of the optical pickup mounted on the optical disk device is exceeded, proper read/write action is disabled, which causes an error during recording or reproduction thus resulting in degradation in the read/write quality.
In order to solve such a problem, a tilt correction method is in use for detecting a tilt in a predetermined area of an optical disk on activation before read/write operation and inclining the optical axis of laser light in accordance with the tilt to correct the tilt.
In accordance with an optical disk, a rise in the temperature in an optical disk device causes a change in the tilt compared with the activation before read/write operation. For example, as shown in the tilt correction flowchart of FIG. 9 supporting a change in temperature (Patent Reference 1), there has been a technique that constantly detects the temperature in the optical disk device by using a temperature sensor provided in an optical disk device, determines whether the change in the temperature has exceeded a predetermined threshold (S101), and in case it is determined that the change in the temperature has exceeded the predetermined threshold, detects a dc component of a focus driving signal (S101) and stores into a memory the relation between the detection result and the radial position (S103). Based on the stored numeric data, the technique re-computes and updates a distortion function and a tilt approximation function (S104) and generates and constantly outputs a tilt driving signal in the current radial position (S105).
With the outputted tilt driving signal, the objective lens of the optical pickup is inclined and the optical axis of the recording layer of the optical disk becomes perpendicular to the optical axis of laser light thus assures favorable recording and reproduction.
In other words, a method has been proposed that detects a tilt again in the presence of a change in temperature and appropriately control tilt correction thus assuring favorable recording and reproduction.
While not shown, another related art technology, a method is proposed that divides an optical disk into a plurality of zones in its radial direction and, in case it is determined that a change in temperature during recording/reproduction with respect to the temperature stored for each zone has exceeded a predetermined threshold, detects a tilt again for each zone and performs tilt correction based on the result (Patent Reference 2).
According to another related art technology, another method is proposed that detects a tilt in the area on the inner circumference alone to perform tilt correction on activation before read/write operation is started. This shortens the time required for activation as well as checks the presence of saved data per area and per temperature when a predetermined change in temperature occurred to determine whether detection of a tilt is required again, thus performing tilt correction more efficiently.
Patent Reference 1: JP-A-2003-281761 (FIG. 26 on Page 37)
Patent Reference 2: JP-A-2005-129119 (FIG. 2 on Page 2)
Patent Reference 3: JP-A-2006-48824 (FIG. 2 on Page 12)
However, in the related art technique, even in the quality of an optical disk is good and distortion of the optical disk is small so that the optical disk is less subject to a change in the optical disk device and is within a permissible tilt range of the optical pickup mounted on the optical disk device, a tilt in a predetermined area is detected and tilt correction is made to offset the tilt each time the change in the temperature has exceeded a predetermined threshold. This prevents processing required for intended recording/reproduction operation from being performed smoothly thus resulting in worse efficiency.
In particular, with an optical disk device, each element such as a spindle motor, a feed motor, a laser diode, or a driving circuit is heated due to its energy consumption during operation after power on. The temporal change in the temperature is large. In case only a temperature width of a temperature threshold value has a small value, the recording/reproduction may be subjected to a being influence when the interruption processing time exceeds the capacity of a buffer memory for temporarily saving recording/reproduction data.